Magnetic media with texturing features formed by selectively non-uniform laser beams

ABSTRACT

Magnetic data storage disks, particularly along dedicated transducing head contact regions, are laser textured according to a process in which beam shaping optical components impart an elliptical or otherwise elongated cross-section to the laser beam. Consequently, individual texturing features such as rims and nodules are elliptical or elongate, with more gradual height gradients in directions parallel to their major axes. The texturing features further are oriented with respect to the direction of transducing head accelerations and decelerations, which yields high performance in terms of reduced dynamic friction, reduced stiction and better wear characteristics. Texturing features are formed in a variety of patterns, including patterns with adjacent features contacting one another. A further refinement involves forming features with substantially different slopes on opposites sides of a maximum height region.

This is a divisional of copending prior application Ser. No. 08/849,001,filed Aug. 13, 1999, and now U.S. Pat. No. 6,225,595 issued on May 1,2001.

This application claims the benefit of Provisional Application Ser. No.60/017,267 entitled “Laser Texture Patterns Formed by Non-AxisymmetricBumps for Magnetic Thin Film Disks”, filed May 13, 1996; and ProvisionalApplication Ser. No. 60/042,341, entitled “Using Wedged Prism to Controlthe Laser-Beam Sectional-Shape for Adjustable Elliptical Bump-Shapes inLaser Texturing Process of Magnetic Recording Media”, filed Mar. 17,1997.

BACKGROUND OF THE INVENTION

The present invention relates to laser texturing of magnetic datastorage media and more particularly to processes for controlling theshapes and orientations of texturing features formed in such texturingprocesses, as well as the resulting storage media.

Laser texturing of magnetic disks, particularly over areas designatedfor contact with data transducing heads, is known to reduce friction andimprove wear characteristics as compared to mechanically textured disks.Texturing involves focusing a laser beam onto a disk substrate surfaceat multiple locations, forming at each location a depression surroundedby a raised rim, as in U.S. Pat. No. 5,062,021 (Ranjan) and U.S. Pat.No. 5,108,781 (Ranjan). Alternatively, as shown in InternationalPublication No. WO 97/07931 published Mar. 6, 1977 (Meyer), the laserbeam also can be used to form a bump or nodule at each of the multiplelocations. In some cases, a dome or bump is surrounded by a ring.

In any event, the individual topographical features are circular oraxisymmetric, more particularly symmetrical about a vertical centralaxis in the case of features formed on a horizontal surface. Whiletextures based on these features exhibit considerable improvement overmechanically formed textures, the ongoing quest for lower transducinghead flying heights and shorter times for accessing data lead to morestringent tribological textures, the ongoing quest for lower transducinghead flying heights and shorter times for accessing data lead to morestringent tribological requirements.

Meeting these requirements has been difficult in view of certainstructural characteristics of the circular, axisymmetric rims andnodules. These features include a relatively small radius of curvature,a relatively large nodule height as compared to diameter, and large rimheight compared to rim width. The resulting abrupt changes in surfaceelevation cause turbulence at the head/media interface. This results inundesirably high levels of acoustic energy at take-off and landing ofthe transducing head, i.e. at disk accelerations and decelerations. Theclosed, rim-like features have exhibited a tendency to collect debris,and their radial component can generate a drag force thought tocontribute to dynamic friction.

Therefore, it is an object of the present invention to provide magneticdata storage media with transducer contact regions textured for improvedwear and reduced dynamic friction.

Another object is to provide a process for using a laser to texture thesurfaces of magnetic data storage media, with more control over theshape and orientation and texturing features formed by the laser toimpart a desired roughness.

A further object is to provide a laser texturing process that affordsmore consistency in forming asymmetrical features such as rims andnodules on textured magnetic media.

Yet another object is to provide magnetic media in which the orientationof non-circular, non-axisymmetric topographical features is determinedwith reference to the direction of transducing head accelerations anddecelerations, to increase the performance benefits derived from theasymmetries.

SUMMARY OF THE INVENTION

To achieve these and other objects, there is provided a process forsurface texturing a magnetic data storage medium, including thefollowing steps:

a. directing a coherent energy beam from a source thereof toward amagnetic data storage medium;

b. locating beam shaping optics between the source and the storagemedium, thereby shaping the beam to provide a shaped beam segment alongwhich sections taken through the beam perpendicular to beam propagationhave a selected non-circular sectional shape; and

c. causing the coherent energy beam to impinge upon a selected surfaceof the storage medium at a plurality of locations thereon, altering thetopography of the selected surface at each of the locations by forming anon-circular texturing feature, while orienting the features with majoraxes thereof substantially aligned in a predetermined direction.

The features formed according to this process are of the same generaltypes as previously mentioned forms, including nodules, bumps and rims,having a smooth, rounded or rotund character that leads to reducedfriction and increased wear. In a departure from prior forms, featuresformed by the present process are non-circular or non-axisymmetric inthe sense of being substantially elongated in a direction parallel tothe major plane of the data storage medium. Thus, the nodules or bumpsare oblong or oval, and the rims are elliptical rather than circular. Ingeneral, each feature has a major or “long” axis in the direction ofelongation and a minor or short axis that is perpendicular to the majoraxis. The aspect ratio, i.e. the major axis/minor axis ratio, can be inthe range of about 1.5 to about 10, and more preferably is in the rangeof about 4-6.

The formation of elongated features provides several advantages. One ofthese, specific to rim-like features is a reduced tendency to entrapmaterial. The elongated, elliptical rims exhibit a height gradient inthe direction of the major axis, from a maximum height along medialregions intersected by the minor axis, to minimal heights at oppositeend regions intersected by the major axis. At sufficient elongation, therim height at these end regions becomes negligible, forminginterruptions or gaps in the otherwise elliptical rim. These gaps allowany material collected within the rim to escape, e.g. during storagemedium accelerations and decelerations.

More generally, all forms of the elongated texturing features exhibitmore favorable profiles when elongated. In particular, each nodule, rimor other feature has a height profile that varies, from a maximum heightgradient or steepest profile in the vertical plane containing the minoraxis, to a minimum height gradient or most gradual profile in the planecontaining the major axis. Other planes yield intermediate gradients andprofiles, with the maximum or minor-axis profile most like that of asimilarly sized but axisymmetric feature.

Thus, a maximum benefit is realized when the elongated topographicalfeatures are correctly oriented, i.e. with their major axes to theextent possible aligned with the direction of transducing head travelrelative to the storage medium during accelerations and decelerations.In disk-shaped storage media, this direction is circumferential withrespect to the disks. As a result of this orientation, the transducinghead, when moving on or over the dedicated contact region, encountersmore gradual changes in height. This reduces turbulence at thehead/medium interface, reduces dynamic friction, reduces stiction, andpermits lower head flying heights. Wear characteristics are improved,because the elongated features, when properly oriented, more effectivelywithstand contact with the transducing head.

The beam shaping optics can take a variety of forms, the most simplebeing a single wedged prism, with a pair of cylindrical lenses beingmore suitable. The most preferred version of beam shaping opticscomprises a pair of complementary wedged prisms. The wedged prisms arepreferred due to their plane surface refraction of the coherent energybeam, which preserves beam collimation and propagation factor M² whileminimizing aberrations and distortions. This enables a smaller focalspot size, suitable for forming smaller texturing features, while alsoenhancing control over the shape of the features.

Regardless of whether wedged prisms or cylindrical lenses are employed,using beam shaping optics to provide a specially shaped, non-circular(in section) laser beam affords effective control over the shape andorientation of elongated texturing features, and affords a high degreeof flexibility in terms of selecting aspect ratios. This is in contrastto tilting the laser beam, a possibility mentioned in the foregoingRanjan patents and Meyer international publication, for which an aspectratio as low as 2 would require a severe tilt of 60 degrees from thepreferred orientation perpendicular to the treated surface. The improvedcontrol and flexibility afforded by optically shaping the laser beamallow a customizing of texturing heretofore unavailable, not only inselecting the degree of elongation, but in the consistency with whichfeatures conform to the desired asymmetry.

IN THE DRAWINGS

For a further understanding of the above and other features andadvantages, reference is made to the following detailed description andto the drawings, in which:

FIG. 1 is a plan view of a magnetic data storage disk and a datatransducing head supported for generally radial movement relative to thedisk;

FIG. 2 is an enlarged partial sectional view of the magnetic disk inFIG. 1;

FIG. 3 is an elevational view of a texturing device for formingtexturing features on the disk;

FIGS. 4A-4D illustrate energy distributions and profiles of acylindrical laser beam and a shaped laser beam, respectively;

FIG. 5 is a perspective view of one of the texturing features, namely anelliptical rim;

FIG. 6 is a top view showing an elliptical rim;

FIG. 7 is a sectional view taken along the vertical plane containing aminor axis of the rim;

FIG. 8 is a sectional view taken along the vertical plane containing amajor axis of the rim;

FIG. 9 is a perspective view showing an oblong nodule;

FIG. 10 is a top view of the elliptical nodule;

FIG. 11 is a sectional view taken along the vertical plane containing aminor axis of the nodule;

FIG. 12 is a sectional view taken along the vertical plane containing amajor plane of the nodule;

FIG. 13 is an enlarged partial top view of the disk showing a pattern oftopographical features formed on the disk;

FIG. 14 is a chart illustrating comparative dynamic friction due toaxisymmetric texturing features versus non-axisymmetric texturingfeatures;

FIG. 15 illustrates an alternative pattern of texturing features;

FIG. 16 illustrates an alternative texturing device;

FIG. 17 illustrates a further alternative laser texturing device;

FIG. 18 illustrates a further alternative asymmetric texturing feature;

FIG. 19 illustrates yet another alternative asymmetric texturingfeature; and

FIG. 20 illustrates a side profile of the feature in FIG. 19.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, there is shown in FIGS. 1 and 2 a mediumfor recording and reading magnetic data, in particular magnetic disk 16rotatable about a vertical axis and having a substantially planar andhorizontal upper surface 18. A rotary actuator (not shown) carries atransducing head support arm 20 in cantilevered fashion. A magnetic datatransducing head 22 is mounted to the free end of the support arm,through a suspension 24 which allows gimballing action of the head, i.e.limited vertical travel and rotation about pitch and roll axes. Therotary actuator and the support arm pivot to move head 22 in an arcuatepath, generally radially with respect to the disk.

At the center of disk 22 is an opening to accommodate a disk drivespindle 26 used to rotate the disk. Between the opening and an outercircumferential edge 28 of the disk, upper surface 18 is divided intothree annular regions or zones: a radially inward region 30 used forclamping the disk to the spindle; a dedicated transducing head contactzone 32; and a data storage zone 34 that serves as the area forrecording and reading the magnetic data.

When disk 16 is at rest, or rotating at a speed substantially below thenormal operating range, head 22 contacts upper surface 18. When the diskrotates within the normal operating range, an air bearing or cushion isformed by air flowing between head 22 and upper surface 18 in thedirection of disk rotation. The air bearing supports the head inparallel, spaced apart relation to the upper surface. Typically thedistance between a planar bottom surface 36 of head 22 and upper surface18, known as the head “flying height”, is about 10 microinches (254 nm)or less. The flying height should be as low as practicable for maximumdata storage density.

For data recording and reading operations, rotation of the disk andpivoting of the support arm are controlled in concert to selectivelyposition transducing head 22 near desired locations within data zone 34.Following a reading or recording operation, the disk is decelerated andsupport arm 20 is moved radially inward toward contact zone 32. By thetime disk 16 decelerates sufficiently to allow head 22 to engage theupper surface, the head is positioned over the contact zone. Thus, headcontact with other regions of the disk surface is avoided. Before thenext data operation, the disk is accelerated from stop, initially withhead 22 engaged with disk 16 within the contact zone. Support arm 20 isnot pivoted until the head is supported by an air bearing, free of thecontact zone.

Magnetic disk 16 is formed first by polishing, grinding or otherwisemechanically finishing an aluminum substrate disk 38 to provide asubstantially flat upper surface. Next, a nickel-phosphorous alloy isplated onto the upper surface of the substrate disk, to provide anon-magnetizable layer 40 with a uniform thickness within the range ofabout 2-10 microns. Following plating, the upper surface of the Ni—Palloy layer, i.e. a substrate surface 42, is polished to a roughness ofgenerally less than about 0.1 microinch (2.54 nm). A saturated cloth,paper or pad coated or flooded with cerium oxide, silicon carbide oranother suitable grit, is used for this purpose. A liquid slurrycontaining grit also may be used. Alternatively, aluminum substratedisks can be obtained with Ni—P alloy layers already applied, thenpolished as described.

After mechanical polishing, substrate disk 38 is laser textured at leastwithin contact zone 32 to provide a desired surface roughness. Lasertexturing involves melting the substrate disk at and near surface 42 atmultiple locations, forming at each location a texturing feature, aswill be described in greater detail below. The texture is influenced bythe general pattern of texturing features, as well as the size and shapeof the features individually.

Fabrication of disk 16 after texturing involves the application ofseveral layers. Chrome is sputter deposited onto substrate surface 42,preferably to a thickness in the range of about 10-100 nm, to form anunderlayer 44. The underlayer is well suited for subsequent depositionof a magnetic thin film, in that the crystalline structure of underlayer44 can control the epitaxy of the crystalline magnetic film. Themagnetic thin film provides a recording layer 46 for storing themagnetic data. The thin film material preferably is acobalt/tantalum/chromium alloy or a cobalt/platinum/chromium alloy, andis sputter deposited to a thickness in the range of about 10-50 nm.Finally, a protective layer 48, typically carbon, is sputter depositedonto the recording layer to a thickness of about 5-30 nm. Underlayer 44,recording layer 46 and cover layer 48 are substantially uniform inthickness. Consequently, upper surface 18 substantially replicates thetexture of substrate surface 42.

Laser texturing preferably is accomplished with a laser texturing device50. As seen in FIG. 3, device 50 includes a spindle 52 for rotatablysupporting substrate disk 38. Above disk 38, a carriage 54 supports alaser module 56 for reciprocal movement radially with respect to thedisk. The laser module includes a naodymium: yetrium lithium fluoride(Nd:YLF) diode laser 58, and collimating optics 60 for collimating thediode laser output to produce a beam 62 in the form of a circularcylinder having a diameter of about 1 mm. With laser 58 preferablyoperated in the TEM₀₀ mode, the beam has a Gaussian energy distributionas indicated in FIG. 4A. Sections of the beam perpendicular topropagation, i.e. horizontal sections as viewed in FIG. 3, exhibitcircular profiles as shown in FIG. 4B.

The laser module also includes several optical components forselectively shaping beam 62, to expand the beam in a first directionwhile leaving the beam substantially unchanged in another directionperpendicular to the first. These components include a pair of wedgedprisms 64 and 66 spaced from one another along the beam path. The prismsare supported by adjustment components, schematically illustrated at 68and 70 respectively, that permit azimuth angle adjustment of each prismabout an axis perpendicular to the plane of the drawing. This permitsadjustment of the angle of incidence α of the laser energy upon a planarreceiving surface 72 of prism 64. Given the non-zero angle α and thealignment of an opposed planar exit surface 74 substantiallyperpendicular to the refracted beam, the beam emerges from prism 64refracted and at an oblique angle relative to the incoming beam in arefracted, partially broadened beam segment 76. Beam segment 76 entersprism 66 through a planar receiving surface 78, refracted and thusangularly offset from the beam propagation direction, preferably by thesame angle of incidence α, but in the opposite direction. An opposedexit surface 80 of prism 66 is substantially perpendicular to therefracted beam. As a result, the beam, having been twice refracted andtwice enlarged in the same direction, emerges from prism 66 as a shapedbeam segment 82. Sections of shaped beam segment 82 perpendicular topropagation have elliptical profiles as indicated in FIG. 4C. Thecircular profile in FIG. 4B illustrates the circular or axisymmetricnature of beam 62 upstream of the beam shaping optics. The beam diameteris constant, regardless of the angle at which it is taken. By contrast,the non-circular, non-axisymmetric shaped beam segment 82 exhibits theelliptical profile of FIG. 4C, with axes ranging from a minor axis “a”taken in the horizontal direction and normal to the plane of FIG. 3, toa major or long axis “b” taken in the horizontal direction parallel tothe plane of FIG. 3. The energy distribution in beam segment 82 remainsGaussian, but like the beam itself is broadened in the directionparallel to the major axis, as shown in FIG. 4D.

Prisms 64 and 66 can be considered complementary in the sense that (1)they have the same size, shape and refractive index and thus refractincident coherent energy by the same amount or same angle; and (2) theyare positioned to refract energy in opposite directions, so that shapedbeam segment 82 is parallel to beam 62 upstream of the shapingcomponents. This feature while not essential is advantageous because itmost effectively preserves the beam collimation and propagation factorM². (The propagation factor M² describes the purity of the TEM₀₀ mode.For a perfect Gaussian beam, M² is equal to 1.)

Azimuth angles of prisms 64 and 66 can be adjusted through components 68and 70 to change the angles of incidence α, and thus change the aspectratio b/a of the shaped beam segment. Through this adjustment to theprisms it has been found practicable to increase the aspect ratio from 1(circular profile) up to about 6. More particularly, the aspect ratio ofshaped beam segment 82, due to the wedged prisms can be determined bythe equation:$\frac{b_{b}}{a_{b}} = \frac{\cos \left\lbrack {\arcsin \left( {\sin \quad {\alpha/n}} \right)} \right\rbrack}{\cos \quad \alpha}$

where α is the angle of incidence and n is the index of refraction (bothprisms).

Beyond the beam shaping optics, a focusing lens 84 converges the beamand defines a focal spot or area 86 of beam impingement onto substratesurface 42. Focal spot 86 has the elliptical shape and aspect ratio ofthe beam section shown in FIG. 4C. The major and minor axes of the focalspot are determined by the following equations: $\begin{matrix}{a_{f} = \frac{4{fM}^{2}\lambda}{\pi \quad b_{b}}} & (2) \\{b_{f} = \frac{4\quad {fM}^{2}\lambda}{\pi \quad a_{b}}} & (3)\end{matrix}$

where a_(f) and b_(f) are the respective minor and major axes of thefocal spot, f is the focal length, and λ is the beam wavelength. Thus,the shape of focal spot 86 is controlled by prisms 64 and 66 and morespecifically their azimuth angles, while the size of the focal spot iscontrolled by focusing lens 84 in conjunction with the prisms, and ofcourse in part by collimating optics 60.

As explained in the aforementioned U.S. Pat. No. 5,062,021, U.S. Pat.No. 5,108,781, and International Publication No. WO 97/07931, whichdocuments are incorporated herein by reference, the focusing of laserenergy onto the metallic surface of the substrate disk causes highlylocalized melting at the surface. Although the material resolidifiesrapidly, there is sufficient material flow to form either a rim or anodule, with higher energy levels tending to result in rims rather thannodules.

FIG. 5 shows in perspective a texturing feature formed using device 50,namely a rim 88. FIGS. 6-8 illustrate the rim profile from the top andfrom two vertical sections through the rim perpendicular to one another.As seen from these views, rim 88 is elongated or elliptical, having anaspect ratio b/a of greater than one. This aspect ratio is notnecessarily proportional to the aspect ratio of the beam and focal spot.However, there is a correspondence, in that within practical limits, theaspect ratio of rim 88 tends to increase with increases in the beam andfocal spot aspect ratio. Typically, rim lengths (major axis b) arewithin the range of about 50 to about 200 microns, with rim widths(minor axis a) in the range of about 15-50 microns. The rim aspect ratioshould be at least about 1.5, and at most about 10. More preferably, theaspect ratio ranges from about 4 to about 6.

In FIG. 7, rim 88 and its adjacent portion of substrate disk 38 areshown in section along the vertical plane containing minor axis a. Theprofile in that plane is substantially the same as the profile resultingfrom a vertical plane taken through a circular or axisymmetric rim ofthe same height. A top edge 90 of the rim is curved, illustrating a keydifference from circular rims in that the rim height is non-uniform.

The sectional view in FIG. 8 is along the vertical plane containingmajor axis b. As compared to FIG. 7, opposite portions of the rim arefarther apart from one another, and the rim sections themselves havemore gradual height gradients. Rim top edge 90 is highest along medialregions 92 of the rim, i.e. regions intersected by the minor axis. Therim top edge slopes downward in both directions toward opposite ends 94and 96 of the rim, i.e. regions intersected by the major axis, where therim height is at its minimum. Thus, in FIG. 8 as compared to FIG. 7, allfeatures have more gradual inclines.

A nodule or bump 98 formed by device 50 is shown in perspective in FIG.9, with corresponding top, end sectional and side sectional views inFIGS. 10-12. Once again, the sectional views are based on verticalplanes through the a and b axes with the profile in FIG. 11 comparableto a profile of a circular bump having the same height, and the profileview in FIG. 12 showing a substantially more gradual incline from amaximum height at the center of bump 98.

Maximum rim heights are typically in the range of 5-30 nm, while maximumnodule or bump heights typically are in the range of 5-30 nm.

Beyond controlling individual rims and nodules, device 50 is used toprovide a desired pattern or distribution of the texturing featuresthroughout contact zone 32. One suitable pattern is a spiral, formed byrotating substrate disk 38 on a vertical axis at an angular speed ω(FIG. 3) while at the same time moving the laser module radially withrespect to the disk. The laser is pulsed to form individual texturingfeatures, either rims or nodules, for example at a frequency in therange of 10,000-80,000 pulses per second. The substrate disk is rotatedto provide a suitable linear velocity, for example about one meter persecond. The disk moves continually during texturing, but for purposes ofindividual feature formation can be considered stationary due to theextremely short duration of each pulse, e.g. about 10 ns.

The resulting pattern of rims 88 can be seen in FIG. 13, showing asegment of contact zone 32. Each rim 88 is aligned with its minor axis“a” in the radial direction (with respect to the substrate disk), andwith its major axis “b” in the circumferential direction. This alignmentor orientation is specifically chosen with reference to the movement ofhead 22 and disk 16 relative to one another, particularly duringaccelerations and decelerations of the head. (While accelerations anddecelerations actually are due to disk rotation, they are commonlydiscussed in terms of circular travel of the transducing head relativeto the disk.) The orientation of rims 88 with their major axes in thecircumferential direction has been found highly favorable, because itpositions the most gradual rim height gradients in the direction of headtravel. This reduces turbulence, reduces stiction and dynamic friction,and permits the head to have a lower flying height above the disk.

The chart in FIG. 14 shows the reduced dynamic friction. A plot 100based on disk 16 shows a dynamic friction of approximately 0.6. Acomparative plot 102, based on circular or axisymmetric texturingfeatures, exhibits a substantially higher dynamic friction above 0.8over most of the 20,000 ccs (controlled start stop) cycle range.

A variety of alternative patterns can be used to realize the aboveadvantages, so long as the individual texturing features are properlyaligned. FIG. 15 shows an alternative pattern in which the locationbetween consecutive features 104 is substantially reduced. Adjacent rimsare connected to one another at their ends, thus to form a substantiallycontinuous spiral track. This can be accomplished either by increasingthe laser firing frequency, reducing the angular speed of the substratedisk, or both. More generally, texturing features can be formed inconcentric rings rather than spiral, or even distributed somewhatrandomly throughout the contact zone, so long as they are aligned withtheir major axes in the circumferential direction.

Another improvement is the reduction in noise or acoustic energy attransducing head takeoff and landing. For mechanically textured disks,the acoustic energy has been found to be about 100 mV. For disks withcontact zones laser textured with circular or axisymmetric texturingfeatures, the acoustic energy is substantially higher, e.g. about 200mV. By comparison, magnetic disks with landing zones laser textured withelliptical features in end-to-end contact as shown in FIG. 15, exhibitacoustic energy of abut 70 mV at takeoff and landing, a substantialreduction compared to previous laser texturing, and a favorablecomparison to mechanical texturing. This significant reduction mostlikely is due to the more gradual texturing feature height gradients inthe direction of head travel, and is likely to allow lower transducinghead flying heights over the contact.

FIG. 16 illustrates and alternative device 105 for forming the texturingfeatures, including a spindle 106 rotatably supporting a substrate 108,a carriage 110 and a laser module 112 moved by the carriage radially ofthe spindle and substrate. Laser module 112 includes a laser 114 andcollimating optics, a single wedged prism 116 for shaping the laser beam118, and a focusing lens 120. While wedged prism 116 is suitable forexpanding the beam in one direction while leaving its direction constantin the other, there is less flexibility in terms of adjusting aspectratios, since each angular adjustment of prism 116 (e.g. to change theangle of refraction) also changes the direction of the shaped beamexiting the prism.

FIG. 17 illustrates a further alternative laser texturing device 122,similar to device 50 with the exception that the beam shaping opticsinclude cylindrical lenses 124 and 126 in lieu of the wedged prisms.Downstream lens 126 has a larger radius of curvature than the upstreamlens. The two lenses are centered on a common axis, so that a shapedbeam segment 128 not only is parallel to incident beam 130, but alsocoaxial. While this can be considered an advantage, in most respectsdevice 50 is preferred, due to the need for and difficulty in achievingperfect alignment of the cylindrical lenses in terms of their centers,distance from one another and orientation. Further, lenses 124 and 126are subject to spherical aberration coma, astigmatism, field curvature,and distortion. Accordingly, it is substantially more difficult indevice 122 to preserve collimation and propagation factor M². Also,because the focal spot is larger than the defraction limit in the caseof the cylindrical lenses, certain texturing features are too small tobe formed using device 122.

FIG. 18 illustrates an alternative rim 132 formed for example usingdevice 50. As an extension of the non-uniform height of electrical rims,it has been found that by using a sufficiently large aspect ratio, therim height at the opposite ends of the ellipse can be made negligible,in effect forming two opposite end gaps 134 and 136 in the rim, or inother words forming two crescent-like sections confronting one another,as indicated at 138 and 140 in FIG. 18.

When properly aligned, rims 132 provide the same advantages as rims 88discussed above, with a further advantage in that rims 132 are open andconsiderably less prone to debris entrapment. The reduced tendency toentrap material is likely to enhance wear characteristics.

FIG. 19 illustrates a further alternative texturing feature in the formof an irregular rim 142. As compared to rim 88, the irregular rim has afurther asymmetry, in that the maximum height regions 144 are offsetfrom the minor axis rather than centered. FIG. 20 illustrates the rimside profile 146. Beneath the profile, an arrow 148 indicates thecircumferential direction of disk rotation, i.e. the opposite to thedirection of transducing head “travel”. The rim profile exhibits arelatively steep slope 150 and a more gradual slope 152. As before, themajor axis of the rim coincides with the circumferential direction. Whenthe disk rotates in the direction shown, the head first encounters themore gradual slope 152. Thus, the benefits achieved by elongating andproperly aligning the texturing features are increased by forming anirregular elongated feature, oriented with reference to head and diskmovement as shown.

The asymmetry as to slope in rim 142 is achieved by adjusting thealignment and relative orientation between wedged prisms 64 and 66, andfocusing lens 84.

Thus in accordance with the present invention, magnetic data storagedisks can be textured, particularly throughout dedicated head contactareas, for more controlled accelerations and decelerations of the head,reduced dynamic friction, and improved resistance to wear. Theseadvantages arise due to a process that affords more control over theshape and orientation of elongated, elliptical or otherwisenon-axisymmetric texturing features. A high degree of consistency isachieved in forming and aligning asymmetrical features. These featureshave a uniform orientation determined with reference to the direction oftransducing head accelerations and decelerations, to maximize theperformance advantages derived from the asymmetries.

What is claimed is:
 1. A device for storing magnetic data, including: amagnetic recording medium including a substrate body formed of anon-magnetizable material and a magnetizable film deposited over thesubstrate body and substantially uniform in thickness, said magneticrecording medium having a substantially planar surface including acontact region adapted for a surface engagement with a magnetic datatransducing head during accelerations and decelerations of thetransducing head due to movement of the magnetic recording medium in apredetermined direction relative to the transducing head; and multipleelongate texturing features formed in the substantially planar surfaceand protruding above a nominal surface plane of the contact region tocollectively define a surface roughness of the contact region, each ofthe texturing features having a major axis in its length direction and aminor axis in its width direction, and further having a gradient in itsheight characterized by a maximum height region and first and second topedge regions extending downwardly and oppositely away from the maximumheight region substantially in said length direction toward first andsecond opposite ends of the texturing feature and terminating at saidfirst and second ends, respectively, wherein the texturing features areoriented with their major axes in the predetermined direction, and thefirst and second ends have substantially the same height.
 2. The deviceof claim 1 wherein: said magnetic recording medium is a rotatable disk,and the predetermined direction is circumferential with respect to thedisk.
 3. The device of claim 1 wherein: the texturing features haveheights, above the nominal surface plane in the range of about 5-30 nm.4. The device of claim 1 wherein: each of the texturing features has alength of at least 1.1 times its width.
 5. The device of claim 4wherein: each of the texturing features has a length in the range of 2-6times its width.
 6. The device of claim 1 wherein: the texturingfeatures include at least one of the features selected from the groupconsisting of: substantially elliptical rims, and pairs of confrontingcrescent-like ridges spaced apart from one another to define gaps atopposite ends thereof.
 7. The device of claim 1 wherein: each of thetexturing features has an asymmetry in height gradiants in thepredetermined direction.
 8. The device of claim 7 wherein: saidasymmetry is characterized by the first top edge region beingsubstantially steeper than the second top edge region.
 9. The device ofclaim 8 wherein: the second top edge region is positioned to encounter atransducing head before the first top edge region when the magneticrecording medium is moved in the predetermined direction relative to thetransducing head.
 10. The device of claim 1 further including: ametallic, non-magnetizable underlayer disposed between the substratebody and the magnetizable film, and having a substantially uniformthickness.
 11. An apparatus for recording and reading magnetic dataincluding the device of claim 1, and further including: a magnetic datatransducing head; means for supporting the transducing head in aselected orientation relative to the recording medium for controlledmovement relative to the recording medium in a direction substantiallyperpendicular to the predetermined direction; and means for moving themagnetic recording medium in the predetermined direction.
 12. Theapparatus of claim 11 wherein: the magnetic recording medium is arotatable disk, and the direction for the controlled movement of thetransducing head is radial with respect to the disk.
 13. The device ofclaim 1 wherein: the texturing features are arranged in a spiralpattern.
 14. The device of claim 1 wherein: the first and second ends ofeach texturing feature substantially coincide with the nominal plane.15. The device of claim 1 wherein: the first and second end of eachtexturing feature are substantially centered on the major axis.
 16. Thedevice of claim 1 wherein: the gradient in height is furthercharacterized by the maximum region and third and fourth top edgeregions extending downwardly and oppositely away from the maximum heightregion in directions substantially perpendicular to the length directiontoward opposite sides of the texturing feature, and the third and fourthtop edge regions have steeper slopes than the first and second top edgeregions.
 17. The device of claim 1 wherein: the texturing featuresinclude elongate nodules.
 18. A substrate for a data storage medium,including: the substrate body formed on a non-magnetizable material andhaving a substantially planar substrate surface, wherein the substratebody is adapted to support a plurality of thin film layers including amagnetizable recording layer, and further is moveable in a predetermineddirection relative to a magnetic data transducing head; and multipleelongate texturing features formed in the substrate body and protrudingabove a nominal surface plane of the substrate surface at leastthroughout a selected region of the substrate surface, to collectivelydefine a surface roughness of the selected region, each of the texturingfeatures having a major axis in its length direction and a minor axis inits width direction, and further having a gradient in its heightcharacterized by a maximum height region and first and second top edgeregions extending downwardly and oppositely away from the maximum heightregion substantially in said length direction toward first and secondopposite ends of the texturing feature and terminating at said first andsecond ends, respectively, wherein the texturing features are orientedwith their major axes in the predetermined direction, and the first andsecond ends have substantially the same height.
 19. A substrate of claim18 wherein: the substrate body is disk shaped, and the predetermineddirection is circumferential with respect to the substrate body.
 20. Thesubstrate of claim 18 wherein: each of the texturing features has alength at least 1.1 times its width.
 21. The substrate of claim 20wherein: each of the texturing features has a length in the range of 2-6times its width.
 22. The substrate of claim 18 wherein: the texturingfeatures include at least one of the features selected from the groupconsisting of: substantially elliptical rims, and pairs of confronting,crescent-like ridges spaced apart from one another to define gaps atopposite ends thereof.
 23. The substrate of claim 18 wherein: the firsttop edge region of each of the features is substantially steeper thanthe second top edge region.
 24. The substrate of claim 23 wherein: thesecond top edge region is positioned to encounter a transducing headbefore the first top edge region when the substrate body is moved in thepredetermined direction relative to the transducing head.
 25. Thesubstrate of claim 18 further including: a metallic, non-magnetizableunderlayer disposed over the substrate surface and having asubstantially uniform thickness; and a magnetizable film disposed overthe non-magnetizable underlayer and having a substantially uniformthickness, whereby an outer surface of the magnetizable filmsubstantially replicates a topography of the substrate surface.
 26. Thesubstrate of claim 18 wherein: the first and second ends of eachtexturing feature substantially coincide with the nominal plane.
 27. Thesubstrate of claim 18 wherein: the first and second ends of eachtexturing feature are substantially centered on the major axis.
 28. Thesubstrate of claim 18 wherein: the gradient in height is furthercharacterized by the maximum region and third and fourth top edgeregions extending downwardly and oppositely away from the maximum heightregion in directions substantially perpendicular to the length directiontoward opposite sides of the texturing feature, and the third and fourthtop edge regions have steeper slopes than the first and second top edgeregions.
 29. The substrate of claim 18 wherein: the texturing featuresinclude elongate nodules.
 30. A magnetic data storage disk, including: arotatable magnetic recording disk including a substrate disk formed of anon-magnetizable material and a magnetizable film deposited over thesubstrate disk and substantially uniform in thickness, the magneticrecording disk having a substantially planar surface including a contactregion adapted for surface engagement with a magnetic data transducinghead during accelerations and decelerations of the transducing head dueto movement of the magnetic recording disk relative to the transducinghead in a circumferential direction; and a means for defining a surfaceroughness of the contact region, including multiple texturing featureselongate in the circumferential direction and protruding above a nominalsurface plane of the contact region, each of the features having a firstgradient in its height characterized by a maximum height region andfirst and second slopes extending oppositely away from the maximumheight region substantially in the circumferential direction, and asecond gradient in its height characterized by the maximum height regionand third and fourth slopes extending oppositely away from the maximumheight region substantially in the radial direction, wherein the thirdand fourth slopes are steeper than the first and second slopes.
 31. Thedisk of claim 30 wherein: the texturing features have heights above saidnominal surface plane in the range of about 5-30 nm.
 32. The disk ofclaim 30 wherein: each of the texturing features has a width in a radialdirection with respect to the disk, and has a length in thecircumferential direction at least 1.1 times the width.
 33. Thesubstrate of claim 32 wherein: the length of each of the texturingfeatures is in the range of 1-6 times the width.
 34. The disk of claim30 wherein: the texturing features include at least one of the featuresselected from the group consisting of: substantially elliptical rims;and pairs of confronting, crescent-like ridges spaced apart from oneanother to define gaps at opposite ends thereof.
 35. The substrate ofclaim 30 wherein: the first slope of each of the features issubstantially steeper than the second slope.
 36. The disk of claim 35wherein: the second slope is positioned to encounter a transducing headbefore the first slope when the magnetic recording disk is moved in thecircumferential direction relative to the magnetic data transducinghead.
 37. The disk of claim 30 further including: a metallic,non-magnetizable underlayer disposed between the substrate disk and themagnetizable film, and having a substantially uniform thickness.
 38. Adevice for storing magnetic data, including: a magnetic recording mediumincluding a substrate body formed of a non-magnetizable material and amagnetizable film deposited over the substrate body and substantiallyuniform in thickness, said magnetic recording medium having asubstantially planar surface including a contact region adapted for asurface engagement with a magnetic data transducing head duringaccelerations and decelerations of the transducing head due to movementof the magnetic recording medium in a predetermined direction relativeto the transducing head; and multiple elongate texturing features formedin the substantially planar surface and protruding above a nominalsurface plane of the contact region to collectively define a surfaceroughness of the contact region, each of the texturing features having amajor axis in its length direction and a minor axis in its widthdirection, and further having a gradient in its height characterized bya maximum height region and first and second slopes extending downwardlyand oppositely away from the maximum height region in directionssubstantially in said length direction toward first and second oppositeends of the texturing feature, said gradient in height being furthercharacterized by the maximum region and third and fourth slopesextending downwardly and oppositely away from the maximum height regionin directions substantially perpendicular to the length direction towardopposite sides of the texturing feature, wherein the texturing featuresare oriented with their major axes in the predetermined direction, andwherein the third and fourth slopes are steeper than the first andsecond slopes.
 39. The device of claim 38 wherein: the first and secondslopes terminate at the first and second opposite ends, respectively,and the first and second ends have substantially the same height. 40.The device of claim 38 wherein: the first and second ends of eachtexturing feature substantially coincide with the nominal plane.
 41. Thedevice of claim 38 wherein: the first and second ends of each texturingfeatures are substantially centered on the major axis.
 42. The device ofclaim 38 wherein: said magnetic recording medium is a rotatable disk,and the predetermined direction is circumferential.
 43. The device ofclaim 42 wherein: the texturing features are arranged in a spiralpattern.
 44. The device of claim 38 wherein: the texturing featuresinclude at least one of the features selected from th group consistingof: substantially elliptical rims, and pairs of confrontingcrescent-like ridges spaced apart from one another to define gaps atopposite ends thereof.
 45. The device of claim 38 wherein: the secondslope is more gradual than the first slope, and is positioned toencounter a transducing head before the first slope when the magneticrecording medium is moved in the predetermined direction relative to thetransducing head.
 46. The device of claim 38 further including: ametallic, non-magnetizable underlayer disposed between the substratebody and the magnetizable film, and having a substantially uniformthickness.